<!DOCTYPE html>
<html>
  <!-- Test: if input has a disabled fieldset ancestor, it is barred from
             constraint validation and should not be affected by :invalid
             pseudo-class. -->
  <link rel='stylesheet' type='text/css' href='style.css'>
  <body>
    <fieldset disabled>
      <fieldset>
        <input class='notinvalid' required>
      </fieldset>
    </fieldset>
  </body>
</html>
